the new cIOS (38r15) should fix NSMBW, but some loaders have issues with it.
Some loaders have a fix for NSMBW running on cIOS r14.
Just installing cIOS'es is pretty harmless, and running loaders off sd card is harmless too. So for your own sake, just try the different cIOS'es and loaders out there and see what you like
I use Usbloader GX, and cIOS 38r15, and that works